You might like to look at Alocrom 1200 (Alodine 1200 outside Europe) which
can be hand-applied to preserve and protect aluminium from corrosion,
retaining its conductivity. I used it for many years in industrial and
military applications, where it is applied more thickly but for our purposes
it produces a pleasant gold colour. You can mix small amounts for small
areas that need protection. Surfaces need to be scrupulously clean first.

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David, G3UNA

2. Is there advantage of winding the coils of copper vs. aluminum? Is it
worth silver plating the copper windings? I'm most likely planning to use
1/4" tubing either way.

Both materials will tarnish (oxidize). Since aluminum is already oxidized,
I would go with it, since we are both in AZ where, until the big one, we
are removed from salt air. Silver plating is a waste, IMHO, and not
necessarily of any benefit. See: http://k6mhe.com/n7ws/Plating.pdf